Rotating screen separator

ABSTRACT

There are disclosed herein equipment and methods for screening and concentrating waste water overflow from combined sewer systems. Exemplary equipment includes a separator employing a substantially cylindrical rotating screen. Influent is piped upwardly into the equipment and deflected outwardly toward the inner surface of the screen in a manner to achieve a desired flow rate and flow pattern of the influent onto the screen. Means are provided for controlling the flow rate and for suitably directing the influent in a plurality of substantially discrete inclined streams toward the inner surface of the rotating screen. The screen is rotated at a speed to achieve a desired centrifugal force. Effluent passes through the screen to an outlet and the remaining concentrate passes to an outlet. A certain amount of the influent splashes from the inner surface of the screen, and is received by a backsplash pan and may be recirculated and rescreened. The screen is in the form of a screen cage having a plurality of removable screen panels for facilitating replacement of damaged screens or changing of screen type or mesh size. Cleaning means is provided for directing a cleaning fluid periodically at the screen. The methods disclosed involve the manner in which the influent, effluent, concentrate and backsplash are handled, and the manner in which the influent is screened to achieve a fluid concentrate which is pumpable to other treatment equipment for ultimate disposal. Additionally, a sequence of influent feed and screen cleaning is described.

United States Patent [191 Mook [ ROTATING SCREEN SEPARATOR [75]Inventor: Philip H. Mook, Huntington Beach,

Calif.

[73] Assignee: Sweco, Inc., Los Angeles, Calif.

[22] Filed: Dec. 20, 1971 [21] Appl. No.: 210,179

Related US. Application Data [63] Continuation of Ser. No. 42,099 June1, 1970,

abandoned.

[52] US. Cl 210/78, 210/197, 210/380 [51] int. Cl. Bold 21/26 [58] Fieldof Search 210/78, 197, 372, 210/380 [56] References Cited UNITED STATESPATENTS 946,476 1/1910 Warner 210/380 X 3,511,373 5/1970 McKibben et al.209/234 Primary ExaminerSamih N. Zaharna Assistant ExaminerF. F.Calvetti Att0rneyl..yon & Lyon [57] ABSTRACT There are disclosed hereinequipment and methods for screening and concentrating waste wateroverflow from [451 July 3,1973

combined sewer systems. Exemplary equipment includes a separatoremploying a substantially cylindrical rotating screen. influent is pipedupwardly into the equipment and deflected outwardly toward the innersurface of the screen in a manner to achieve a desired flow rate andflow pattern of the influent onto the screen. Means are provided forcontrolling the flow rate and for suitably directing the influent in aplurality of substantially discrete inclined streams toward the innersurface of the rotating screen. The screen is rotated at a speed toachieve a desired centrifugal force. Effluent passes through the screento an outlet and the remaining concentrate passes to an outlet. Acertain amount of the influent splashes from the inner surface of thescreen, and is received by a backsplash pan and may be recirculated andrescreened. The screen is in the form of a screen cage having aplurality of removable screen panels for facilitating replacement ofdamaged screens or changing of screen type or mesh size. Cleaning meansis provided for directing a cleaning fluid periodically at the screen.The methods disclosed involve the manner in which the influent,effluent, concentrate and backsplash are handled, and the manner inwhich the influent is screened to achieve a fluid concentrate which ispumpable to other treatment equipment for ultimate disposal.Additionally, a sequence of influent feed and screen cleaning isdescribed.

8 Claims, 13 Drawing Figures [451 .July 3,1973

United States Patent [191 Mook PAIENIEDJUL 3 ma snmlurs PATENTEUJUL 3I973 sum 3 or 6 7 PATENTEUJUL 3 I975 SHEET t (If 6 PAIENTEDJuL 31m sums0r 6 ROTATING SCREEN SEPARATOR CROSS REFERENCE TO RELATED APPLICATIONSThis a continuation of application Ser. No. 42,099, filed June 1, 1970,now abandoned.

The concepts disclosed herein are related to those disclosed incopending application Ser. No. 640,241, filed May 22, 1967, now U.S.Pat. No. 3,539,008, entitled Screening Apparatus Employing RotatingCylindrical Screen and Stationary Feed Means, and U.S. Pat. No.3,511,373, both of which are assigned to the assignee of the presentapplication and the disclosures of which are incorporated herein byreference. Briefly, said application Ser. No.-640,241 disclosesapparatus involving a rotating substantially cylindrical screen incombination with a stationary distribution means for screening aninfluent. The screen and distribution means may be used in combinationwith a downstream planar vibratory separator for further screening ofthe concentrate from the rotating screen. Said Pat. No. 3,51 1,373discloses apparatus similar to that in said application and is directedto means for facilitating cleaning of said rotating screen.

Reference is also made to related applications, filed concurrentlyherewith, Ser. No. 42,098, (Lyon & Lyon Docket 132/171 entitled Up-FlowSeparator, filed in the name of Theodore R. Westfall; Ser. No. 42,165,(Lyon & Lyon Docket 132/172), entitled Improved WastewaterConcentration, filed in the name of Walter .1. Talley, Jr.; and Ser. No.42,100, (Lyon & Lyon Docket 132/184), entitled Wastewater Concentration,filed in the name of Walter J. Talley, Jr. and Howard W. Wright, Jr.These applications contain a similar disclosure to that set forthherein, but include claims directed to various of the structural andoperational features disclosed herein.

BACKGROUND OF THE INVENTION This invention relates to the screening of aliquidand solids, and more particularly to screening of storm water,sewage or storm water overflow from combined sewer systems.

Although the present inventive concepts are useful in screening variousmaterials, they have particular application for water polution controland, thus, will be described in this environment and particularly forfinemesh screening for primary treatment of storm water overflow fromcombined sewer systems. As set forth in a research report on treatmentof storm water overflow entitled Rotary Vibratory Fine Screening ofCombined Sewer Overflows" prepared by Cornell, Howland, Hayes andMerryfield in connection with Dept. of the Interior Contract 14-12-128and dated March 1970, the majority of the existing combined sewersthroughout the nation do not have adequate capacity during heavy stormperiods to transport all waste and storm-caused combined flows to atreatment facility. The overflow is bypassed to a receiving stream, thuscausing pollution in the nations water courses.

As further described in said report, the Federal Water Pollution ControlAdministration published a report in 1967 reviewing the effects andmeans of correcting combined sewer overflows on a national basis. Of thetwo hundred million people residing in the United States, approximatelyone hundred and twentyfive million are served by combined or separatesewer systems, and of the one hundred and twenty-five millionapproximately 29 percent are served by combined sewers. Combined sewersare designed to receive all types of waste flows, including storm water,for ultimate treatment at a treatment facility. In determining the sizeof the combined sewer, it has been common engineering practice toprovide capacity for three to five times the dry-weather flow. Duringintensive storm periods, however, the storm-caused combined flow may betwo to one hundred times the dry-weather flow, making overflowconditions unavoidable. To compound the problem, most treatmentfacilities are not designed to handle the hydraulic load of the combinedsewer and, therefore, are required to bypass a portion of thestorm-caused combined flow to protect the treatment facility andtreatment process from damage. The nations treatment facility bypassflows an average estimated 350 hours during the year, or about 4 percentof the total operation time. The pollutional impact of the storm-causedcombined overflow on the waters of the nation has been estimated asequivalent to as much as percent the strength of the domestic sewagebiochemical oxygen demand. This amount creates a major source ofpollution for the nations water courses. The Cornell et al. reportfurther describes certain tests, results and recommendations withrespect to the use of high-rate fine-mesh screens for primary treatmentof storm water overflow from combined sewer systems, the equipmentdescribed being similar to that disclosed in said application Ser. No.640,241 and Pat. No. 3,51 1,373. The present inventive concepts involvecertain improvements thereover.

In light of the foregoing, it is a principal object of the presentinvention to provide improved screening equipment and methods.

A further object of this invention is to provide an improved screeningdevice employing a rotating screen and distribution means associatedtherewith.

Another object of this invention is to provide an improved screeningarrangement for a rotating screening device.

A further object of this invention is to provide an improved screeningdevice employing a rotating screen and means for receiving and recyclingbacksplash from said screen.

Other objects and features of the present invention will become apparentthrough a consideration of the following description and attacheddrawings.

SUMMARY OF THll INVENTION There is disclosed herein a screeningapparatus, such as for use in screening of storm water overflows fromsewer systems, comprising a substantially cylindrical rotary screendevice disposed for rotation within a housing, feed means for directingan influent toward the inner surface of the screen, and outlet means forreceiving (a) the effluent which passes through the screen, (b) theconcentrate which does not pass the screen, and (e) backsplash from thescreen.

The feed means includes an upwardly extending feed pipe, or the like,for supplying the influent to the screen. The feed means may includeadjustable means for varying the rate of flow of influent, and deflectormeans may be provided for directing the flow of influent as a pluralityof substantially discrete inclined streams toward the inner surface ofthe screen.

The rotary screen is in the form of a substantially cylindrical cage andincludes a plurality of screen panels, which may be removed for repair,cleaning or replacement with different mesh screens or different screencloth. The speed of rotation of the screen is selected to provide adesired centrifugal force, or g-loading, of influent on the screen, theg-loading being a function of the radius of the screen and the square ofthe rpm thereof. The velocity of flow of influent onto the screen isselected within a preferable range below which suitable impingement doesnot occur, and above which excessive splashback and possible screendamage may occur. A typical flow velocity is in a range aroundapproximately 13 to feet per second, and exemplary preferred screenspeeds are approximately 65 rpm for a 60 inch diameter screen and 88 rpmfor a 36 inch diameter screen, it being appreciated that other suitableflow velocities, screen speeds, diameters, and the like may be employedwithout departing from the present concepts.

The influent preferably is screened to achieve a relatively fluidconcentrate, as distinguished from a dry concentrate, so that the samemay be readily transported or pumped for further treatment or disposal.

A screen cleaning apparatus is provided for spraying cleaning fluidthrough the screen at desired intervals. In the screening of aninfluent, it is preferable to cyclically (a) feed the influent for apredetermined period of time, (b) terminate the feed, (c) spray thescreen with a cleaning fluid for a shorter predetermined period, and (d)return the feed of influent. An exemplary cycle includes feedinginfluent for four and one-half minutes and cleaning the screen forone-half minute, including a cleaning spray from outside to inside ofthe screen for a few seconds and then inside to outside of the screenfor a few seconds.

Although a complete screening apparatus and methods involving a numberof novel concepts and structures are disclosed herein, the applicationis particularly directed to an improved rotating screening device andhandling of backsplash of influent from the screening device, as well asparticular screen constructions for the screening device; whereas, saidother applications filed concurrently herewith are directed to othernovel features disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectionalelevational view of a preferred screening apparatus;

FIG. 2 is a top plan view of the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view of the apparatus taken along a line 3-3of FIG. 1;

FIGS. 4A and 4B are cross-sectional views illustrating an adjustableinfluent plate of the apparatus of FIG.

FIG. 5 is a perspective view of a distribution dome of the apparatus ofFIG. 1;

FIG. 6A is a top view and FIGS. 6B and 6C are fragmentarycross-sectional views of the distribution dome of FIG. 5;

FIG. 7 is a partial perspective view of a rotary screen cage of theapparatus of FIG. 1;

FIG. 8 is a partial top view of the screen of FIG. 7; and

FIGS. 9A and 9B are views illustrating the manner in which screen panelsare secured to the screen cage of FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS Turning now to the drawings, andparticularly to FIGS. 1 through 3, a rotary screening device isillustrated including an outer substantially cylindrical housing 10containing a rotary screen cage 11, an influent inlet feed pipe 12, aninfluent impingement plate or diverter 13, a drive assembly 14 for thescreen cage 11, an effluent outlet 15, a concentrate outlet 16, and abacksplash outlet 17. It should be noted at this point that FIG. 1 is anelevational cross section view taken along a line 1-1 of FIG. 3;whereas, FIG. 3 is a crosssectional plan view taken generally along aline 33 of FIG. 1.

As will be more fully explained subsequently, an influent, such as stormwater overflow having enormous amounts of water and relatively littlesolids, is fed to the feed pipe 12 and deflected outwardly by theimpinge ment plate 13 toward the inside of the rotating screen cage 11.The screen cage includes a plurality of screen panels, and the influentis screened resulting in a highly liquid effluent and a concentratewhich is substantially less liquid but flowable. The effluent isdischarged by outlet 15 and the concentrate is discharged by outlet 16.The screen cage 11 is rotated at a speed to provide a suitablecentrifugal force for the screening action, and the impingement plate 13is positioned to provide the desired-flow rate of influent toward thescreen cage. A distribution dome 18 may be provided to direct theinfluent as a plurality of substantially discrete inclined flows towardthe inner surface of the screen cage. Influent which splashes back fromthe inner surface of the screen cage may be redirected to the cage formore complete screening, as by collecting the backsplash and recyclingthe same with incoming influent. The upflow of influent provided by thefeed pipe 12 simplifies the design and construction of the apparatus andgenerally involves less fluid head loss than encountered with a feed ofinfluent to the screen cage from above the apparatus.

These screening concepts serve to reduce pollution caused, for example,by overflow of combined stormsanitary sewage systems during periods ofheavy rain fall. As much as one third of the sewage solids settle to thebottom of large combined sewers and in periods of heavy rain, they flowinto streams, lakes, rivers and costal waters without treatment. Thus,during storm peaks, up to percent of the untreated sanitary sewage mayoverflow into receiving waters. As a result, combined treatment systemsoften loose more pollutants to their rivers and streams than they takeout in the treatment plant itself.

As will appear from the following description and drawings, the presentapparatus and concepts meet many storm-sanitary pollution controlrequirements for a compact, low cost, high volume, primary treatmentsystem. The present apparatus is capable of releaving a combined sewagesystem of its hydraulic overload during storm periods, while sending apollutant concentrate to the treatment plant. Exemplary apparatus isapproximately 7 feet in diameter and 6 feet high and employsapproximately nine to 18 removable screen panels on a revolving screencage. A combination of high velocity influent flow and centrifugal forcecan allow approximately 90 to 95 percent of a hydraulic flow of threemillion gallons per day to pass through the screens. The remainingconcentrate containing a high percentage, such as 99 percent, of thefloatable and settleable solids is discharged separately into thehydraulically relieved sewage system.

Considering the construction of the apparatus in more detail, thehousing includes a base 20, a substantially cylindrical upstanding wall21, and covers 22 and 23 to provide a substantially closed container.The screen drive assembly is secured to the top of the apparatus andincludes a mounting plate 24 for supporting a motor, only the base 25thereof being seen in the drawings, and a gear box 26. Suitable supportand spacing plates 27 through 29 are provided to which an I- beam 30with gussets 31 and 32 are secured to form a bearing mount. A pair ofbearings 33 and 34 are secured to the bearing mount. A shaft 35 isjournaled in the bearings 33 and 34 and has a drive pulley 36 affixed atthe upper end thereof. A pulley 37, as seen in FIG. 2, is coupled withthe output shaft of the gear box 26, and the pulleys 36 and 37 arecoupled by means of V- belts 40 and 41. An idler 42 may be provided tomaintain proper belt tension. As will be apparent to those skilled inthe art, the motor is coupled with the input shaft of the gear box 26 inany suitable manner, as by V-belts, and drives the shaft 35 through thebear box, pulleys 37 and 36, and the V-belts 40 and 41. A collar 43 issecured, as by welding, to the lower end of the shaft 35, and the screencage 11 is attached to this collar to enable the shaft 35 to rotate thescreen cage 11.

The wall 21 of the housing 10 extends upwardly as indicated at 44. Thecover 22 may be a lift-off cover, and includes windows 45 as seen inFIG. 2 to enable observation of the interior of the apparatus. Aremovable access door cover 46 may be provided. The wall 21 of thehousing 10 may include a window 47 for observation of the interior ofthe apparatus. Suitable bracing is provided within the housing forstructural purposes and for firmly supporting the various pipes. Anangle bracket 48 and braces 49, for example, are provided as illustratedin FIGS. 1 and 3.

The screen cage 11 will be described in more detail subsequently, butgenerally includes a cage formed of a lower angle ring 50, an upper barring 51, and a plurality of upstanding bars 52 extending between theangle ring 50 and bar ring 51 as best seen in FIGS. 7 and 8. Nine bars52 have been used for an exemplary cage approximately 36 inches indiameter. Support ribs 53 are connected between the various bars 52 anda central collar 54 which is secured to the collar 43 affixed to theshaft 35. Removable screen panels 56 having a frame and screeningmaterial of metal or cloth secured thereto are inserted between thevertical bars 52 and clamped thereto in a substantially sealedrelationship.

As noted earlier, an influent to be screened is supplied through theinfluent pipe 12 and directed upwardly toward the impingement plate 13.The plate deflects the flow outwardly toward the inner surface of thescreen panels 56 of the screen cage 11. The vertical position of theplate 13 is adjustable as will be explained subsequently so as tocontrol the rate of flow of influent. The distribution dome 18 as bestseen in FIGS. 1 and 5 is secured to the upper end of the pipe 12. Thisdome 18 includes a sleeve 60 which rests on a collar 61-affixed to thepipe 12, and a plurality of inclined plates 62 secured to the outersurface of the sleeve 60. A portion 63 of each plate may be bentupwardly as shown in FIG. 5, or separate spacers may form the portions63, and secured to the underside of the next succeeding plate so as toform a rigid structure. The distribution dome 18 functions to directinfluent, which has been deflected by the impingement plate 13, intosubstantially inclined streams toward the inner surface of the screenpanels. An interior wall or divider 66 which is substantiallycylindrical is secured within the housing and extends almost up to thehorizontal surface of the flange of the angle ring 50. This dividerforms, in combination with the housing wall 21, an annular chamber 67for receiving effluent and directing the same to the effluent outlet 15.The effluent, as is known to those skilled in the art, is the materialwhich passes through the screen cage 11. The divider 66 also encloses aconcentrate chamber or bowl 68 which has an inclined bottom 69 fordirecting concentrate to the concentrate outlet 16.

A back-splash pan 71 is positioned within the chamber 68 and coupledwith a support 72. The pipe 17 communicates with the interior of the pan71. The top of the pan 71 is approximately at the elevation of thebottom of the screen panels and the radius of the upper portion of thepan 71 is slightly smaller than the interior diameter of the screen cage11 so as to receive influent which splashes back from the inner surfaceof the screen cage 11 and screen panels 56. The radius of the pan 71typically may be about 2 inches less than the radius of the screen cage11. Concentrate flows through the gap between the interior of the cageand the exterior of the pan 71 to the chamber 68.

The purpose of the backsplash pan 71 is to enable any influent whichsplashes from the screen cage 11 to be collected for either recyclingwith incoming influent or sent to another separator device for screeningto ensure that the maximum desired split between effluent andconcentrate is achieved. Alternatively, other methods of collectingbacksplash may be provided, as for example a baffle below thedistribution dome 18 which catches or otherwise deflects the backsplashmaterial back toward the inner surface of the screen panels at the lowerportion of the screen cage 11. In a test with a 2200 gallon per minuteinfluent flow with no screen panels in the screen cage, it was foundthat 46 gallons of concentrate was collected in the concentrate chamber68. It is believed that this occurred because of backsplash from thescreen cage bars 52. By recycling or further screening of this 46gallons of backsplash in a normal operation with screens it has beencomputed that the split would be improved by 2 percent or better.

Turning again to the influent impingement plate 13, the same isadjustable up and down as noted earlier. The purpose of this adjustmentis to enable control of an orifice area 75 between the lower surface ofthe plate 13 and upper end of the sleeve 60 of the distribution dome 18,or upper end of the pipe 12 in the event the same extends above thesleeve 60. This allows control of the rate of flow of influent. Theplate 13 is secured to a rod 76 which extends upwardly through the shaft35 as seen in FIGS. 1 and 5a and 4b. The upper end of the rod 76 isthreaded into a threaded bushing 77 which is secured to the upper end ofthe shaft 35. The rod 76 thus may be adjusted up or down to vary theposition of the plate 13 with respect to the upper end of the sleeve 60,and may be locked in position by a locknut 78. With the constructionthus described, the plate 13 rotates with the screen cage 11, but may bemade stationary if desired by other suitable supporting structure.

The shape of the plate 13 may be other than flat, such as a segment of asphere. However, it is desired that the flows of influent toward theinner surface of the screen cage 11 be substantially perpendicular tothe inner surface of the screen panel 56 rather than significantlyinclined upwardly or downwardly as viewed in FIG. 1. If these flows aresharply inclined downwardly, the concentrate is excessively liquid; but,on the other hand, if the flows are precisely horizontal and thusperpendicular to the inner surface of the screen panels the flows do notfan out sufficiently to give a wide sweeping flow onto the inner surfaceof the screen panels. Accordingly, it is desired that the flow ofinfluent be almost perpendicular to the inner surface of the screenpanels but at a slight downward angle to obtain a divergent flow, orfan-out of the flow, by the time the influent hits the screen panels.Each flow of influent should fan out to anywhere from substantially theentire height of the screen panels to approximately one-half the heightof the screen panels, or slightly less such as to provide an impingementarea of influent onto the screen panels about 6 inches high. Thus, it isdesired that the flows fan-out slightly, but still flow substantiallyhorizontally from the orifice 75, the fanning-out being accomplished bythe distribution dome 18 into essentially discrete inclined streams. Ifonly a portion of the height of the screen panels is swept by theinfluent flows, the panels can be turned over end-for-end after a periodof use to maximize screen life.

As noted earlier, the majority of the existing combined sewersthroughout the nation do not have adequate capacity during heavy stormperiods to transport all waste and storm-caused combined flows to atreatment facility. The overflow is bypassed to a receiving stream, thuscausing pollution problems. One of the principal applications of thepresent apparatus is in screening enormous amounts of water with solids,such as storm overflow, to separate out the solids and provide arelatively fluid, as distinguished from dry, concentrate which can thenbe properly handled by a sewage treatment facility. The effluent can besuitably disposed of, as for example in a stream. In this manner, theenormous amounts of water do not overtax the sewage treatment facility,while still enabling proper treatment of the maximum amount of solidsfrom the overflow.

One of the principal objectives is to achieve a high split, that is,ratio of effluent (screened product) to concentrate (unscreenedproduct), while still obtaining a slightly fluid concentrate which canflow continuously from the apparatus and be supplied, as by pumping, tosubsequent primary treatment equipment without the problems involved inhandling a solids concentrate. A typical ratio is better than 95 to withthe apparatus described herein and with a typical influent flow of about1,000 gallons per minute. A number of factors affect this split, one ofthe principal factors being the centrifugal force involved in thescreening operation, which varies as the square of the screen cage rpmand as a direct function of the radius thereof. There is a band ofoptimum performance in terms of centrifugal force. It has been foundthat a centrifugal force of around 3 gs appear to be optimum inachieving the maximum split, although it is to be understood that theforce can be below or above this value somewhat. This approximate forceor band around 3 gs can be obtained with a screen cage speed ofapproximately rpm for a screen cage about 60 inches in diameter, andapproximately 88 rpm for a screen cage about 36 inches in diameter.Substantially higher speeds do not improve the split. Additionally,other factors are important in achieving the maximum split, and theseinclude the velocity of the feed of influent, such as approximately 13to 15 feet per second, which can be selected by varying the size of theorifice through adjustment of the plate 13; directing of the flows ofinfluent substantially perpendicular to the inner surface of the screencage as noted earlier; recycling or other screening of backsplash fromthe screen cage; maintaining the screen panels clean; and theorientation of the screen cloth in the screen panels.

The centrifugal force is important in achieving the maximum force on thesolid and water particles for separation of the water from the solids,but must not be excessive because the solids will then tend to cling tothe screen and bing or clog the screen and, additionally, screen damagemay result from high forces. At the optimum force or band of force, theconcentrate flows by gravity down from the screen. The provision ofalmost perpendicular influent flow to the inner surface of the screen isimportant as noted earlier so as to achieve the maximum separation withthe minimum of backsplash or other deflection of influent from thescreen cage. As to flow velocity, if the same is too low, insufficientinfluent reaches the screen. if too high, excessive backsplash occurs,and the high forces may cause premature damage to the screens. Thebacksplash represents unscreened influent, much of which is believed tobe deflected from the bars 52 of the screen cage, and it is desired torecycle or otherwise further screen the backsplash to optimize thesplit. It will be apparent that the screen panels must be clean toachieve the best screening action, and a cycle of influent feed andspray cleaning with a cleaning fluid is preferred as will be describedsubsequently.

The orientation of the screen cloth within the cage is important from awear-life standpoint. It is preferable that the screen cloth be biasmounted to form the screen panels 56 of FIG. 7 rather than positioningthe cloth such that the wires or thread of the screen cloth runvertically and horizontally. The bias mounting disposes the wires orthread at substantially 45 angles re sulting in better screen lifebecause the screen wires are stressed and flexed equally and uniformlyby the flows of influent. This longer life allows the screen cage to runlonger with less down-time therefor improving the efficiency ofscreening. Also, the slope of the inclined plates 62 of the distributiondome 18 affects the height of which the flows impinge on the screenpanels and, thus affects screen life. A 6 inch drop at the edge of theplate where the radial length of the plate is 28 inches gives a slope of2] percent which has been found suitable for a 60 inch diameter cage.

Furthermore, it is believed that the direction of rotation of the screencage with respect to the inclination of the plate 62 of the dome 18 maycontribute to obtaining the most efficient screening operation. Thedirection of rotation of the screen cage 11 is preferably as indicatedwith respect to the screen panel 56 illustrated in FIG. 5 (counterclockwise) and as illustrated with respect to the screen cage in FlG. 8.Referring again to FIG. 5, the flows of influent leave the inclinedplates 62 of the distribution dome 60 at substantially the angle of theplates 62 and continuously aid in sweeping large solid particles fromthe rotatingscreen.

Screen cleaning is achieved by means of supply pipes 80 and 81 havingrespective groups of nozzles 82 and 83. The nozzles 82 and 83 providesprays of cleaning fluid through the screen panels. It is preferred tofeed influent for a period of time, such as 4% minutes to minutes, stopthe flow of influent and spray the screen panels with a cleaning fluidsuch as hot water containing a hypochlorite solution for one-fourth to 1minute, and then continue to feed the influent. This operation continuescyclically, with the cleaning period lasting, for example, one-halfminute, with a spray from the nozzles 82 for seconds and then from thenozzles 83 for seconds. It is desired to clean the screens before theyget dirty which can be measured in terms of degradation of the split,for example, down to 90-to-l0.

Turning again to the screen cage, and particularly FIGS. 7 through 9,preferably the screen panels 56 are removable for repair or replacement,and can be readily locked in place in the screen cage. Channels forreceiving the edges of the screen panels 56 are provided by T-brackets85 which are secured to the bars 52 by threaded stubs 86 and 87 andrespective wing nuts 88 and 89. Braces 91 are secured between adjacentribs 53, and a gasket 92 is affixed onto each brace 91 to form a sealwith the top of each respective screen panel 56. The edges of the frame93 of the screen panel 56 which abut with the bars 52 may have a bead ofresilient material 94 thereon to form a seal between the screen panelsand bars 52. The panel includes an angle frame and the screen fabric maybe secured thereto with an epoxy adhesive. Exemplary screen fabric is165 TBC providing 47 percent open area. Metal or synthetic fabrics canbe used. Stainless steel fabric has been found suitable. A removablecover 95 having a removable section 96 may be provided for the top ofthe screen cage.

A vent pipe 97 may be provided to vent the interior of the housing 10 tothe atmosphere. A plate 98 is attached to the shaft 35 above the coverportions 22 and 23 of the housing. Operation of the screening apparatuscauses a higher pressure area toward the periphery of the screen cage11, and air is drawn in between the plate 98 and cover portions 22-23and vented by the vent pipe 97. This blow of air past the plate 98 aidsin maintaining the bearings 33 and 34 clean and moisture free. The plate98 prevents material from splashing onto the bearings from the coverportions 22-23 where the shaft 35 extends therethrough.

The following represent exemplary test data from the screening ofinfluent by apparatus like that described 36 inch screen cage, theactual inside diameter defined by the inner surface of the screen panelsbeing approximately 30 inches. Table 1A sets forth data obtained with alarge orifice 75 opening; whereas, the data in Table 1B involvesvariations in the orifice 75.

TABLE [A Feed Approx. Average General Test G.P.M. RPM ConcentrateComments No. 1 1,000 105 8.3% 26 gpm splashback 2 1,000 0 2.3% Noscreens-not rotating 3 1,005 120 0.8% No screens-rotating 4 1,000 601.3% No screens 5 1,000 72 1.2% No screens 10 6 1,000 93 1.0% No screens7 1,000 78 1.0% No screens- 8 1.000 0 2.2% No screens not rotating 1.00078 1.0% No screens 10 1.000 0 12.0% 7-165 TBC panels.

' 2-165/4 panels 11 1,000 78 8.6% 7165 TBC panels. 2-165/4 panels 121,500 78 13.4% 7-165 TBC panels, 2-165/4 panels 13 650 78 9.2% 7-165 TBCpanels, 2-l65/4 panels 14 1,000 0 15.0% 7-Yb 165 TBC panels, 2-105Dacron panels 15 1,00 87 8.6% 7-165 TBC panels, 2-hb Dacron panels TABLEIB Test Approx. Feed Average General G.P.M. RPM Orifice Concen- C tratemen's 16 1,000 90 W 4.3% Screens as above- 40 ft/sec feed velocity 171,000 90 36 2.0% 15 ft/sec feed velocityz 3 g.s e.f. 18 1,000 90 1 turn20 1,000 90 1 T 2.0% 21 1,000 90 %AT 2.0% 22 1,000 90 %%T 2.0% 23 1,00090 %+/4T 1.93% 24 1,000 90 1%T 1.76% 25 1,000 90 %+1%T 1.67% 26 1,000 9056+1%T 1.88% 27 1,000 90 %+1 T 1.76% 28 1,000 90 %+1% T 2.00% 29 1.00090 %+5/6 T 1.71% 30 1,000 fi+5l6 T 1.67% 31 1.000 60 /4+% T 2.3% 321,000 90 13/16 1.7%

250 PPM Paper Pulp Solution 33 1,000 90 13/16 5.0% 34 1,000 90 13/167.7% (Dirty Screens) Tests 1 through 32 are on a clean water influent,and tests 33 and 34 involve an approximately 250 part per million paperpulp solution. As is apparent from Tables IA and 18, a split of 8.3 to8.6 percent was obtained in tests 1 through 15 on clean water; however,the feed impingement velocity was well under 10 feet per second.Commencing with test No. 16, changes were made in the impingement plate13 adjustment and thus represent performance in terms of concentratesplit at different orifice openings and rpms. The references under thefeed orifice column to +1 turn, 1 T, and so forth refer to turns of therod 76 which was threaded nine turns per inch. Test No. 25 representsthe best performance in terms of concentrate split. Test No. 30indicates that no substantial improvement in split was gained byincreasing the rpm above 90 rpm. Ninety rpm for this apparatus providesabout 3 gs of centrifugal force which also has been found to besubstantially optimum for a 60 inch separator'unit operating at 65 rpm.Likewise no substantial improvement was found in test No. 31 at 60 rpm.

It should be noted that 124 rpm gives over 6 gs and sixty rpm gives lessthan 2 gs for the approximately 30 inch diameter screen involved.Although a useful split is obtained, more optimum operation occurs,consistent with maximum screen life and obtaining a slightly wetconcentrate, when the centrifugal force is nearer to 3 gs. However, itis intended herein by reference to approximately 3 gs centrifugal forceto refer to a band of centrifugal force around 3 gs such as l to 7 g's,but preferablY closerto 3 gs.

The following Tablell includes data wherein the influent was raw sewage,and summarizes 14 test runs of the same unit. Initial tests utilizing a165 fusion bonded four mesh screen indicated a concentrate split rangingfrom 6 to 8 percent. Later runs with bias mounted 165 TBC screensindicated a substantial improvement in split as compared with the fusionbonded 165/4. Test No. 6 is not believed to be representative becausethe influent was of unusual character. The 165 TBC screen panelsprovided the best performance at approximately 90 rpm as can be seenfrom Table 11. It should be noted that the concentrate volume in bothtest Nos. 8 and 9 at the lower 62 rpm increased substantially ascompared with the 90 rpm cage speed. Also, test Nos. 10 and 11 at 124rpm indicate a wetter concentrate than at 90 rpm. The screen was cleanedin a cyclic manner as previously described. It will be noted that anincrease in concentrate split was obtained by using the bias mount 165TBC screen panels as compared to fusion bonded panels. Similar resultsin split have been obtained with similar apparatus 4 having anapproximately 60 inch diameter screen cage.

TABLE 11 Control Feed led Approx. Feed Average Type of Test g p m rpmOpen Concentrate Screen No. ing (too short screen) 1 1,000 83.5 36 6.0%165/4 fusion bonded 2 1,000 83.5 A 8.0% 16514 bonded 3 1,000 103 /4 6.5%16514 bonded 4 1,000 103 6.5% 16514 bonded 5 1,000 59 56" 7.5% 16514bonded 6 1,000 86 2.9% 165 TBC (abnormal feed) 7 1,000 86 3.0% 165 TBC(more nonnal feed) 8 1,000 6 56" 3.8% 165 TBC 9 1,000 62 55 3.5% 165 TBC10 1,000 124 5 8 3.1% 165 TBC 11 1,000 124 A4 2.9% 165 TBC 12 1,000 9056 2.85% v 165 TB 13 1,000 90 56 3.25% 5-l65 TBC panels 4-165/4 bondedpanels 14 1,000 90 56" 5.0% All panels 165/4 bonded The presentembodiments of this invention are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated-by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims therefore are intended to be embraced therein.

What is claimed is:

1. Screening apparatus comprising support means,

a rotary substantially cylindrical screen structure supported by saidsupport means for screening an influent to derive an effluent and aconcentrate, said screen structure including a cage and a plurality ofsubstantially flat screen panels coupled therewith with each of saidscreen panels including screening material having threads mounted on abias with respect to the axis of said cage for allowing said threads tobe stressed and flexed equally and uniformly by flows of the influent,

drive means coupled with said screen structure for rotating said screenstructure, and 1 feed means for feeding said influent toward the innersurface of said screen structure.

2. Apparatus as in claim 1 wherein said threads of said screeningmaterial are disposed at approximately 45 with respect to the axis ofsaid cage.

3. A method of screening an influent containing substantial amounts ofliquid and relatively few solids, such as storm water overflow,employing a rotating substantially cylindrical screen structurecomprising flowing said influent to within said screen structure,

deflecting said influent outwardly toward the inner surface of saidscreen structure to derive an effluent and-a concentrate, said screenstructure having means causing an amount of said influent to bedeflected inwardly from said inner surface,

separately collecting said concentrate and said influent deflectedinwardly from said inner surface, and

returning the inwardly deflected influent toward said screen structureand screening same with said screen structure.

4. Screening apparatus comprising support means,

a rotary substantially cylindrical screen structure supported by saidsupport means for screening an influent to derive an effluent and aconcentrate, said screen structure having an inner surface,

drive means coupled with said screen structure for rotating said screenstructure,

feed means for feeding said influent toward the inner surface of saidscreen structure,

collector means disposed below said screen structure for receiving saidconcentrate, and

separate collector means mounted for receiving influent which isinwardly deflected from said inner surface of said screen structure, andmeans coupled with said separate collector means for returning suchinwardly deflected and collected influent to the incoming influent toallow screening thereof by said screen structure.

5. Apparatus as in claim 4 wherein said separate collector meansincludes pan means mounted below said screen structure and extendingsubstantially to the inner surface of said screen structure.

6. Apparatus as in claim 4 wherein said screen structure comprises acage and a plurality of substantially flat screen panels coupledtherewith, each of said screen panels including screening materialhaving threads mounted on a bias with respect to the axis of said cage.

7. Apparatus as in claim 6 wherein said threads are disposed atapproximately 45 with respect to the axis of said cage.

8. Apparatus as in claim 4 including I deflector means mounted withinsaid screen structure for deflecting the flow of influent as a series ofsubstantially discrete inclined flows toward the inner surface of saidscreen structure, said deflector means including a plurality of inclinedplates, and

said screen structure being rotated by said drive means in the directionof downward incline of said plates.

l 1 l i l

2. Apparatus as in claim 1 wherein said threads of said screeningmaterial are disposed at approximately 45* with respect to the axis ofsaid cage.
 3. A method of screening an influent containing substantialamounts of liquid and relatively few solids, such as storm wateroverflow, employing a rotating substantially cylindrical screenstructure comprising flowing said influent to within said screenstructure, deflecting said influent outwardly toward the inner surfaceof said screen structure to derive an effluent and a concentrate, saidscreen structure having means causing an amount of said influent to bedeflected inwardly from said inner surface, separately collecting saidconcentrate and said influent deflected inwardly from said innersurface, and returning the inwardly deflected influent toward saidscreen structure and screening same with said screen structure. 4.Screening apparatus comprising support means, a rotary substantiallycylindrical screen structure supported by said support means forscreening an influent to derive an effluent and a concentrate, saidscreen structure having an inner surface, drive means coupled with saidscreen structure for rotating said screen structure, feed means forfeeding said influent toward the inner surface of said screen structure,collector means disposed below said screen structure for receiving saidconcentrate, and separate collector means mounted for receiving influentwhich is inwardly deflected from said inner surface of said screenstructure, and means coupled with said separate collector means forreturning such inwardly deflected and collected influent to the incominginfluent to allow screening thereof by said screen structure. 5.Apparatus as in claim 4 wherein said separate collector means includespan means mounted below said screen structure and extendingsubstantially to the inner surface of said screen structure. 6.Apparatus as in claim 4 wherein said screen structure comprises a cageand a plurality of substantially flat screen panels coupled therewith,each of said screen panels including screening material having threadsmounted on a bias with respect to the axis of said cage.
 7. Apparatus asin claim 6 wherein said threads are disposed at approximately 45* withrespect to the axis of said cage.
 8. Apparatus as in claim 4 includingdeflector means mounted within said screen structure for deflecting theflow of influent as a series of substantially discrete inclined flowstoward the inner surface of said screen structure, said deflector meansincluding a plurality of inclined plates, and said screen structurebeing rotated by said drive means in the direction of downward inclineof said plates.